Cancer metastasis involves a complex series of steps in which cancer cells leave the original tumor site and migrate to other parts of the body via the bloodstream, the lymphatic system, or by direct extension. Metastasis is a very important indication of the malignancy and development stage of a tumor. However, metastatic cancer is difficult to assess because patients with metastatic cancer do not have symptoms or they have symptoms that are also common to other diseases. Therefore, there are continuing needs to develop novel methods to detect sarcoma metastasis.
The ERM protein family includes ezrin, radixin and moesin. ERM proteins are primarily expressed in cytoplasm, concentrated in actin rich cell-surface structures. They act as structural linkers between the plasma membranes and actin-based cytoskeletons. The ERM proteins share high degrees of inter-species and inter-molecular homologies. The ERM proteins typically have three domains: a N-terminal domain called FERM domain (band four-point-one, ezrin, radixin, moesin homology domain) because of its homology with the band 4.1 protein, a central helical domain and a C-terminal domain. The C-terminal domain binds F-actin while the N-terminal domain is responsible for binding to adhesion molecules in the plasma membrane (Louvet-Vallee (2000)). Several lines of evidence have indicated that NH2— and COOH-terminal domains of ERM proteins are associated intra- and/or intermolecularly in the cytoplasm, which suppresses their binding ability to integral membrane proteins and actin filaments, respectively (Ken Hayashi et al., J. Cell Sci. 112:1149-1158 (1999)).
Moesin is localized in filopodia and other membranous protrusions that are important for cell-cell recognition and signaling and for cell movement (see Louvet-Vallee, Biol. Cell 92:305-16 (2000)). The human moesin protein contains 577 amino acids and typically consists of three domains: the N-terminal FERM domain, the central helical domain and the C-terminal domain. Furthermore, human moesin protein shares high degrees of sequence homology with moesins from other species such as mouse and bovine moesins (Sato et al. Cell Sci. J. 103:131-143(1992)).